Current LCD display panels require that light be directed through the edge lit panel reflecting off of the back surface of the panel and emitted out of the front surface of the panel. The LCD panel itself is formed of a matrix of very small, referred to as pixel, openings also referred to as LCD gates. When a gate is switched open, light passes through until the gate is switched off. In color displays, each pixel is composed of three sub pixels which are Red, Blue, and Green. When all three sub pixels are switched on, the three colors appear to be emitted from the same point and the eye sees white light. When the sub pixels are switched on and off for various time periods the light emitted from the three sub pixels appears as various colors.
Edge lit back light systems are composed of one or more light guides as shown in prior art FIGS. 1 and 12 of U.S. Pat. No. 7,963,687, to further direct the light from the light guide(s) and diffuse the light before it is allowed to enter the LCD panel. If the light is not diffused, distortions in the light, called pattering, would appear making the light output of the LCD panel distorted and unsightly.
Edge lit back light assemblies may also have air gaps between the LED emitters and the surface of the light guide that receives the light. The air gap is intended to allow the emitted light to spread and mix prior to entering the light guide structure. The light guides are typically composed of one or more plastic like panels selected for their specific light transmissive and reflective properties. These panels will typically have reflective films or materials on all of the edges with the exception of the portion of the edge where light is emitted into the panel to ensure that as much light as possible is available to be emitted out of the front of the panel toward the LCD display panel.
The back surface of an edge lit LED panel light guide is designed such that the guide panel emits light in one direction only, from the back surface of the panel to the front surface of the panel where it is emitted. The back surface of the panel, prior art FIGS. 3 and 5 from U.S. Pat. No. 7,963,687, will typically be reflective or contain structures that reflect and redirect light to the front surface of the light guide panel. Those light guides with reflective back surfaces may be made so by any of a number of means including plated coatings and reflective films. Light guides lacking a plated or reflective film on the back surface may have reflective structures, '687 FIGS. 4A through 4D, pressed or molded into the back surface. These structures may be comprised of prisms and or lens as shown in the prior art figures. Light guides lacking a reflective back surface or a back surface with reflective structures may have an additional sheet of reflective structures adhered around it's perimeter with an air gap between the sheet and the back surface of the light guide. These sheets of reflective structures are typically prisms and or lens as shown in the prior art figures.
Diffuser panels, prior art FIG. 3 reference 27, are placed between the light guide assembly and the back surface of the LCD panel. Light emitted from the front surface of the light guide assembly will have some patterning regardless of the reflective films, prisms and lens and other films and structures to minimize light patterning. A diffuser is used to further blend the light from the light guide into a uniform beam before the light enters the LCD panel. So as to ensure a homogenous beam, an air gap is generally present between the front surface of the diffuser and a polarizer sheet or film and the back surface of the LCD array panel. The air gap between the diffuser and the polarizer sheet gives the light leaving the diffuser a better opportunity to mix resulting in an attenuation of any remaining pattering.
Polarizers
The last part of a backlight assembly is a polarizer sheet. The polarizer is composed of one or more films that contain very specific polarization properties. LCD panels are composed of LCD light gates where the gate material is a polarized element. If the light entering the gate is not polarized, some of the light will be attenuated because it will not be in phase with the polarized LCD pixel gate. If the light entering the gate is polarized, then the light entering the LCD gate will be less attenuated. In order to ensure that light entering the LCD panel from the diffuser is polarized, a polarizer film(s) is placed between the front surface of the diffuser and the back surface of the LCD array panel. An air gap will generally be present between the emitting surface of the diffuser and the polarized film.